The present invention relates generally to electromagnetic radiation sources, and more particularly to a phased array source of electromagnetic radiation.
Magnetrons are well known in the art. Magnetrons have long served as highly efficient sources of microwave energy. For example, magnetrons are commonly employed in microwave ovens to generate sufficient microwave energy for heating and cooking various foods. The use of magnetrons is desirable in that they operate with high efficiency, thus avoiding high costs associated with excess power consumption, heat dissipation, etc.
Microwave magnetrons employ a constant magnetic field to produce a rotating electron space charge. The space charge interacts with a plurality of microwave resonant cavities to generate microwave radiation. Heretofore, magnetrons have been generally limited to maximum operating frequencies below about 100 Gigahertz (Ghz). Higher frequency operation previously has not been considered practical for perhaps a variety of reasons. For example, extremely high magnetic fields would be required in order to scale a magnetron to very small dimensions. In addition, there would be considerable difficulty in fabricating very small microwave resonators. Such problems previously have made higher frequency magnetrons improbable and impractical.
Recently, the applicant has developed a magnetron that is suitable for operating at frequencies heretofore not possible with conventional magnetrons. This high frequency magnetron is capable of producing high efficiency, high power electromagnetic energy at frequencies within the infrared and visible light bands, and which may extend beyond into higher frequency bands such as ultraviolet, x-ray, etc. As a result, the magnetron may serve as a light source in a variety of applications such as long distance optical communications, commercial and industrial lighting, manufacturing, etc. Such magnetron is described in detail in commonly assigned, copending U.S. patent application Ser. No. 09/584,887, filed on Jun. 1, 2000, now U.S. Pat. No. 6,373,194, and Ser. No. 09/798,623, filed on Mar. 1, 2001, now U.S. Pat. No. 6,504,303, the entire disclosures of which are both incorporated herein by reference.
This high frequency magnetron is advantageous as it does not require extremely high magnetic fields. Rather, the magnetron preferably uses a magnetic field of more reasonable strength, and more preferably a magnetic field obtained from permanent magnets. The magnetic field strength determines the radius of rotation and angular velocity of the electron space charge within the interaction region between the cathode and the anode (also referred to herein as the anode-cathode space). The anode includes a plurality of small resonant cavities which are sized according to the desired operating wavelength. A mechanism is provided for constraining the plurality of resonant cavities to operate in what is known as a pi-mode. Specifically, each resonant cavity is constrained to oscillate pi-radians out of phase with the resonant cavities immediately adjacent thereto. An output coupler or coupler array is provided to couple optical radiation away from the resonant cavities in order to deliver useful output power.
Nevertheless, there remains a strong need in the art for even further advances in the development of high frequency electromagnetic radiation sources. For example, there remains a strong need for a device with fewer loss mechanisms and hence even further improved efficiency. More particularly, there is a strong need for a device which does not utilize a plurality of small resonant cavities. Such a device would offer greater design flexibility. Moreover, such a device would be particularly well suited for producing electromagnetic radiation at very short wavelengths.
A phased array source of electromagnetic radiation (referred to herein as a xe2x80x9cphaserxe2x80x9d) is provided in accordance with the present invention. The phaser converts direct current (dc) electricity into single-frequency electromagnetic radiation. Its wavelength of operation may be in the microwave bands or infrared light or visible light bands, or even shorter wavelengths.
In the exemplary embodiments, the phaser includes an array of phasing lines and/or interdigital electrodes which are disposed around the outer circumference of an electron interaction space. During operation, oscillating electric fields appear in gaps between adjacent phasing lines/interdigital electrodes in the array. The electric fields are constrained to point in opposite directions in adjacent gaps, thus providing so-called xe2x80x9cpi-modexe2x80x9d fields that are necessary for efficient magnetron operation.
An electron cloud rotates about an axis of symmetry within the interaction space. As the cloud rotates, the electron distribution becomes bunched on its outer surface forming spokes of electronic charge which resemble the teeth on a gear. The operating frequency of the phaser is determined by how rapidly the spokes pass from one gap to the next in one half of the oscillation period. The electron rotational velocity is determined primarily by the strength of a permanent magnetic field and the electric field which are applied to the interaction region. For very high frequency operation, the phasing lines/interdigital electrodes are spaced very closely to permit a large number of gap passings per second.
According to one particular aspect of the invention, an electromagnetic radiation source is provided. The source includes an anode and a cathode separated by an anode-cathode space. Electrical contacts are provided for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space. At least one magnet is arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field. A plurality of openings are formed along a surface of the anode which defines the anode-cathode space, whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings. The source further includes a common resonator which receives electromagnetic radiation induced in the openings as a result of the electrons passing in close proximity to the openings, and which reflects the electromagnetic radiation back towards the openings and produces oscillating electric fields across each of the openings at a desired operating frequency.
According to another aspect of the invention, an electromagnetic radiation source is provided which includes an anode and a cathode separated by an anode-cathode space. The source further includes electrical contacts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space. In addition, the source includes at least one magnet arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field, and an array comprising N pin-like electrodes forming at least a part of the anode and arranged in a pattern to define the anode-cathode space. Furthermore, the source includes at least one common resonant cavity in proximity to the electrodes. The electrodes are spaced apart with openings therebetween, and electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings to establish a resonant electromagnetic field within the common resonant cavity.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.